Polysaccharide gum and process for its manufacture

ABSTRACT

Processes are disclosed for the purification and recovery of polysaccharide gums from an aqueous solution, particularly xanthan gum from a fermentation broth. An aqueous solution of at least one polysaccharide gum is mixed with a non-solvent stream comprising water and a subprecipitant level of a non-solvent of the polysaccharide gum. The mixture is concentrated to increase the polysaccharide gum concentration, and optionally undergoes a heat treatment. Additional non-solvent is added to the concentrated mixture to precipitate the polysaccharide gum. The precipitated gum is dried after being separated from the liquid component of the mixture. The removed liquid component can be recycled to the earlier step in the process in which the polysaccharide gum solution is mixed with the non-solvent stream.

BACKGROUND OF THE INVENTION

This application is a divisional of application 10/152,873, filed on May21, 2002, which issued as U.S. Pat. No. 6,881,838 on Apr. 19, 2005.

1. Field of the Invention

The present invention relates generally to recovering a polysaccharidegum from an aqueous fluid in which the gum is dissolved. Moreparticularly, it relates to methods involving concentration,heat-treatment, and precipitation of a polysaccharide gum, and topolysaccharide gums recovered using such methods.

2. Description of Related Art

Certain polysaccharide gums (e.g., xanthan gum), which arehydrocolloids, are used in food, pharmaceutical, industrial, and oilfield applications, because of their rheology. Addition of certainpolysaccharide gums in foods can aid in making water-based productsthicker, creamier, more visually appealing, and more stable over a widerrange of temperature, pH and time. In non-food related applications,certain polysaccharide gums can provide viscosity for suspension,improved stability, and/or thickening of fluids. For example, in oil andgas drilling, certain polysaccharide gums can be used to modify therheology of a fluid and to enhance the efficiency of drilling, workover,and completion operations.

Certain useful polysaccharide gums are extracted from plant material.For example, carrageenan is extracted from certain species of the classRhodophyceae (red seaweed). Microorganisms can produce certainpolysaccharide gums. Xanthan gum, for example, is a polysaccharide thatcan be produced by fermentation using bacterium of the Xanthomonas sp.Gellan gum is the generic name of a polysaccharide that can be producedby cultured Pseudomonas elodea or related organisms. Curdlan is apolysaccharide gum that can be produced by a microorganism (e.g.,Alcaligenes faecalis varmyxogenes). Still other polysaccharide gums canbe produced either by extraction from plant material or by microbialfermentation. Alginate is a polysaccharide gum that can be obtained byextraction from certain species of seaweed, or alternatively Azotobactervinelandii or Pseudomonas aeruginosa can be used to produce thepolysaccharide gum through fermentation.

Certain processes for the recovery and purification of polysaccharidegums (such as alginate, carrageenan, xanthan, pectin, gellan, welan,pullulan, curdlan, rhamsan, and sphingan polymers) from an aqueous fluidin which they are dissolved rely on a water-miscible non-solventprecipitation of the gum, such as an alcohol precipitation, amongothers. The aqueous fluid can comprise polysaccharides that are theproducts of microbial fermentation or extraction from a plant material.For example, isopropanol, ethanol, or acetone (e.g., water-misciblenon-solvents of xanthan gum) can be used to precipitate xanthan gum fromaqueous solution. In certain cases, the addition of salt(s) oradjustment of pH can reduce the amount of non-solvent required forprecipitation of a polysaccharide gum. Following precipitation the gumcan be dewatered and dried.

Recovery of a polysaccharide gum can be a difficult and expensiveprocess, because polysaccharide gums can be viscous even at lowconcentrations, making handling difficult. Thus, mixing of reagents withthe gum can be a power intensive process. The relatively lowconcentration of gum in fermentation broth (often less than about 5%)and in extracts from plant materials, as well as the high cost ofcertain gum non-solvents, and the losses associated with distillation ofthe gum non-solvent significantly impact the cost of processingpolysaccharide gums.

Research to improve processes for the recovery of polysaccharide gumsdissolved in aqueous fluid has focused on methods of reducing the amountof gum non-solvent needed to precipitate gum. Such methods haveinvolved:

-   -   1. increasing gum concentration in an aqueous fluid comprising        dissolved polysaccharide gum prior to non-solvent addition        (e.g., via improved fermentation/extraction methods that achieve        higher yield and concentration of the polysaccharide or via        concentrating the extracts or fermentation products);    -   2. adding multivalent cations to an aqueous fluid comprising        certain dissolved polysaccharide gums in order to increase        precipitation efficiency, and reduce the amount of non-solvent        that must be added; and    -   3. in addition to adding multivalent cations to an aqueous fluid        comprising certain dissolved polysaccharide gums, adjusting its        pH in order to increase precipitation efficiency, and reduce the        amount of non-solvent that must be added.        Such methods have their drawbacks. As stated above, it can be        difficult to work with concentrated polysaccharide gum        solutions, because even at relatively low concentrations of        polysaccharide gum (less than about 5%), the solutions can be        extremely viscous and difficult to handle. It can be difficult        to remove biomass from polysaccharide gum fluids having        relatively high concentrations of the polysaccharide gum that        are obtained through methods involving fermentation processes.        Furthermore, addition of cations and pH adjustment can result in        the production of polysaccharide gum products (e.g., salts of        polysaccharide gums) that have reduced solubility. Therefore,        there is a long-standing need for improved processes for        recovering polysaccharide gums.

SUMMARY OF THE INVENTION

Certain embodiments of the present invention are directed to methods ofrecovering at least one polysaccharide gum from an aqueous fluid.Methods of the present invention can be performed either as batchprocesses or continuous processes. In certain embodiments thepolysaccharide gum is selected from the group consisting of xanthan gum,welan, gellan, pullulan, carrageenan, alginate, pectin, rhamsan, curdlanand sphingan polymers. The aqueous fluid comprises water and betweenabout 1 wt % and 10 wt % of at least one polysaccharide gum that issubstantially dissolved in the aqueous fluid (e.g., at least about 95 wt% of the polysaccharide gum present in the fluid is dissolved). Theaqueous fluid can also comprise at least one impurity and in certainembodiments the impurity is a soluble impurity. The polysaccharide gumcan be (1) a product of fermentation, (2) a compound extracted from aplant, or (3) a dried polysaccharide gum dissolved in aqueous solution,wherein the dried polysaccharide gum was recovered by a processpreviously performed.

The aqueous fluid is mixed with an organic non-solvent stream comprisingwater and an organic non-solvent to produce a first mixture. The aqueousfluid can be concentrated, by filtration for example, before mixing itwith the organic non-solvent stream. The organic non-solvent is anon-solvent for the polysaccharide gum that is to be recovered from theaqueous fluid, and in certain embodiments it can be selected from thegroup consisting of isopropyl alcohol, methanol, ethanol, acetone, andother solvents of similar polarity, as well as mixtures thereof. Thus,the organic non-solvent can comprise a mixture of organic compounds.

The first mixture comprises a sub-precipitant concentration of theorganic non-solvent (the concentration of the organic non-solvent isbelow the minimum level at which the polysaccharide gum begins toprecipitate from solution), water, and dissolved polysaccharide gum. Incertain embodiments in which the polysaccharide gum is xanthan gum andthe organic non-solvent is isopropyl alcohol, the sub-precipitant amountof organic non-solvent in the first mixture can be between about 5 and45% by weight of the first mixture.

The first mixture is concentrated, thereby increasing the polysaccharidegum concentration. Impurities soluble in at least one of the aqueoussolution or the organic non-solvent can also be removed by theconcentration step. Thus this concentration step yields a concentratedfirst mixture and a stream of components removed from the first mixture.In certain embodiments the concentration of the first mixture isachieved by filtration using methods known in the art. The stream ofremoved components comprises water, any soluble impurities present, andnon-solvent.

After concentration, the organic non-solvent concentration in the firstmixture is still at a sub-precipitant level. An additional amount oforganic non-solvent is mixed with the concentrated first mixture,thereby producing a second mixture. As additional organic non-solvent ismixed with the first mixture, some of the polysaccharide gum mayprecipitate before a precipitating concentration of non-solvent isachieved throughout the second mixture. The second mixture comprises (A)a liquid component comprising organic non-solvent and water, wherein theorganic non-solvent concentration in the second mixture is sufficient toprecipitate a majority of the polysaccharide gum present in the secondmixture, and (B) precipitated polysaccharide gum.

In certain embodiments, the stream of removed components can bedistilled to recover organic non-solvent that can also be recycled andused (1) as a component of the organic non-solvent stream or (2) as atleast a portion of the additional amount of organic non-solvent that ismixed with the concentrated first mixture to achieve precipitation ofthe polysaccharide gum.

In certain embodiments, the second mixture is separated into a firstfraction and a second fraction. This can be accomplished bycentrifugation, decanting or methods of solid/liquid separation known inthe art. The first fraction comprises a majority of the liquid componentand the second fraction comprises substantially all of the precipitatedpolysaccharide gum. The first fraction can then be recycled as acomponent of the organic non-solvent stream to be mixed with the firstaqueous fluid in subsequent rounds of the process. The second fractioncan be (a) dried directly to produce a first dried polysaccharide gumproduct (e.g., comprising less than about 12 wt % water), or (b)optionally, the second fraction can be washed with organic non-solventor a solution of water and organic non-solvent prior to drying. Organicnon-solvent and water driven off as the second fraction is dried can beadded to the organic non-solvent stream mixed with the first aqueousfluid to produce the first mixture. In other embodiments at least someof the organic non-solvent and water driven off during drying can becondensed, filtered, and distilled to recover organic non-solvent, andthe distilled organic non-solvent can be used as a component of thesecond mixture. In certain embodiments, the method further comprisestreating the first mixture at a temperature and for a time sufficient tocause at least some increase in the viscosity of the polysaccharide gum.The heat treatment can be performed at least one of before, after, orduring concentrating the first mixture, and before the precipitationstep. The first dried polysaccharide gum product recovered using methodsdescribed above involving a heat treatment can be a heat-treated firstdried xanthan gum product.

Upon rehydration of the heat-treated first dried xanthan gum product itcan have a viscosity that is at least 10% greater than that of arehydrated second dried xanthan gum product prepared by a methodcomprising, providing a second aqueous fluid comprising water andxanthan gum having the same or similar composition as that provided forpreparing the first dried xanthan gum product. The second aqueous fluidis heat treated at the same temperature and for the same duration as thefirst mixture in preparing the first dried xanthan gum product. Next theheat-treated second aqueous fluid is mixed with sufficient organicnon-solvent to produce a third mixture. The third mixture comprises (A)a liquid component comprising the organic non-solvent and water, whereinthe organic non-solvent concentration in the third mixture is sufficientto precipitate a majority of the xanthan gum present in the thirdmixture, and (B) a second precipitated xanthan gum. The third mixture isseparated into an A fraction and a B fraction, wherein the A fractioncomprises a majority of the liquid component and the B fractioncomprises substantially all of the second precipitated xanthan gum.Finally, the B fraction is dried to produce a second dried xanthan gumproduct. Thus, the heat treatment used in preparing the second driedxanthan gum product is not performed on a fluid comprising an organicnon-solvent, as is the case with the heat treatment used in preparingthe first dried xanthan gum product.

Certain embodiments of the present invention are directed to methods ofrecovering xanthan gum from an aqueous fluid. The aqueous fluidcomprises between about 1 wt % and 10 wt % dissolved xanthan gum. Theaqueous fluid is mixed with an organic non-solvent stream comprisingwater and an organic non-solvent of xanthan gum, thereby producing afirst mixture. The first mixture comprises a sub-precipitantconcentration of the organic non-solvent. The xanthan gum in the firstmixture is concentrated (for example, by filtration of the firstmixture) by removal of at least some of the water, soluble impurities ifpresent, and the non-solvent (e.g., the stream of removed components).The stream of removed components can be distilled to recover organicnon-solvent. Distilled organic non-solvent can be recycled and used (a)as a component of the organic non-solvent stream or (b) as at least aportion of the additional amount of organic non-solvent that is mixedwith the concentrated first mixture to achieve precipitation of thexanthan gum.

After concentrating the first mixture, the organic non-solventconcentration is still below the minimum concentration at which thexanthan gum begins to precipitate. The first mixture is heated to atemperature of between about 90° C. and about 125° C. for at least aboutfive minutes, and this heat treatment can occur at least one of before,after or during the step of concentrating the first mixture, and beforethe precipitating step. When the organic non-solvent of the xanthan gumsolution is isopropyl alcohol, isopropanol can comprise between about 5and 45% by weight of the first mixture. Additional organic non-solventis then mixed with the first mixture, thereby producing a secondmixture. The second mixture comprises (A) a liquid component comprisingthe organic non-solvent and water, wherein the organic non-solventconcentration in the second mixture is sufficient to precipitate amajority of the xanthan gum present in the second mixture, and (B)precipitated xanthan gum. The second mixture can be separated into afirst fraction and a second fraction, wherein the first fractioncomprises a majority of the liquid component and the second fractioncomprises substantially all of the precipitated xanthan gum.

In certain embodiments, the second mixture is separated into a firstfraction and a second fraction, as described above, and the secondfraction can be dried, or washed and dried to produce a dried xanthangum product. In certain embodiments, the dried xanthan gum product, whenrehydrated in water, has a viscosity that is at least 10% greater than arehydrated dried xanthan gun product that has been produced byalternative methods using heat treatment. The separated first fractioncan be recycled, as described above to produce a first mixture.

Certain embodiments of the present invention directed to xanthan gumrecovery can yield high quality xanthan gum, which meets the foodchemical codex requirements for xanthan gum, and which has a viscosityin excess of 800 cps at 0.25% ds when measured on a Brookfieldviscometer with a #4 spindle at 60 rpm and 75 degrees F. An improvementin the viscosity of a heat-treated xanthan gum of at least 100%(doubling the viscosity of an untreated gum) can be achievedconsistently using certain embodiments of the present invention.

Polysaccharide gums recovered by methods of the present invention canhave fewer color impurities than polysaccharide gums recovered usingknown methods. Furthermore, methods of the present invention can reducethe amount of distilled non-solvent that is needed to process andrecover polysaccharide gums, and thus, can reduce both the capital andoperating costs associated with distillation of organic non-solvents.Certain embodiments of the present invention which are directed to therecovery and processing of xanthan gum can result in precipitated gumbeing dried in a desirable form comprising somewhat discrete fibrousstrands as opposed to gelatinous balls. Methods of the inventioninvolving heat treatments can aid in maximizing improvements inviscosity for polysaccharide gums and in achieving consistent viscosityincreases, particularly in xanthan gum recovery processes.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofspecific embodiments presented herein.

FIG. 1 is a process flow diagram of an embodiment of the presentinvention.

FIG. 2 is a process flow diagram of a process used for the recovery of apolysaccharide gum from an aqueous fluid involving distilled organicnon-solvent.

FIG. 3 depicts the effect of isopropanol content during heat treatmentof xanthan gum in broth for 20 minutes at 90 degrees Celsius.

FIG. 4 depicts the effect on viscosity of a xanthan gum depending on thetemperature used during heat treatment.

FIG. 5 depicts the effect on viscosity of a xanthan gum depending on thetemperature used during heat treatment and the concentration of thexanthan gum in solution without isopropanol.

FIG. 6 depicts the effect on viscosity of a xanthan gum depending on thetemperature used during heat treatment and the concentration of thexanthan gum in solution with isopropanol.

FIG. 7 depicts the effect on viscosity of a xanthan gum depending onwhether the isopropanol used in the heat treatment is distilledisopropanol or recycled isopropanol.

FIG. 8 depicts the effect on viscosity of a xanthan gum depending onlength of heat treatment.

FIG. 9 depicts a comparison of fermentation broths, broths heat-treatedin a conventional manner without IPA, and those heat-treated using amethod of the present invention wherein the broth is heat-treated afterthe addition of IPA.

FIG. 10 depicts the effect on viscosity of xanthan gums in aqueoussolution heat treated with or without isopropanol.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The process of the present invention can be used to recover a variety ofpolysaccharide gums from aqueous fluid. The process is especially wellsuited for recovery of xanthan gum, welan, gellan, pullulan,carrageenan, alginate, pectin, rhamsan, curdlan and sphingan polymers(e.g., S657, S7, S198, S88, NW11, and I-886, among others). Xanthan gumhas a polymer backbone made up of β-1,4-linked D-glucose residues, andit has a trisaccharide branch made up of one glucuronic acid unitbetween two mannose units. The trisaccharide branch is linked to everyother glucose unit in the polymer backbone at the number 3 position.Welan gum has a backbone composed of tetra saccharide units comprisingD-glucose, D-glucuronic acid, D-glucose, and L-rhamnose, and the sidechain consists of a single L-mannose or a single L-rhamnose unit. Gellanis a microbial polysaccharide, comprising a polymeric backbone havingrepeating tetra-saccharide units of glucose, glucuronic acid, glucoseand rhamnose. Pullulan is a linear 1,4:1,6-α-D-glucan, consisting mainlyof maltotriosyl units linked α-1,6 to the next maltotriosyl unit.Pullulan also comprises a small percentage of maltotetraosyl units,which are irregularly distributed within the polysaccharide. Carrageenanis a hydrocolloid consisting mainly of the potassium, sodium, magnesium,and calcium sulfate esters of galactose and 3,6-anhydro-galactosecopolymers. Alginate is made up of two five carbon polymers, mannuronicacid and guluronic acid. The ratio of the acids varies in differentalginates. Pectin is a methylated ester of polygalacturonic acid.Rhamsan has the same backbone as gellan and welan gums, but carries adisaccharide sidechain, while curdlan is a (1,3)-β-D-glucan.

Processes of the present invention can recover at least onepolysaccharide gum from a fermentation broth, a plant extract, or anaqueous solution of a dried polysaccharide gum previously processed anddissolved. Thus, the polysaccharide gums can be fermentation products,solutions of compounds extracted from plant material, or solution ofpolysaccharide gums commercially available.

Preferably, the polysaccharide gum is xanthan gum that is produced byfermentation of a bacterium of Xanthomonas sp, particularly Xanthomonascampestris. Certain fermentation methods to produce xanthan gum involvepropagating a Xanthomonas campestris strain from a slant culture througha standard inoculation train, and inoculating a bioreactor with a seedculture at a level of 2 to 10%. Certain xanthan gum fermentation methodsinvolve growing the culture at a neutral pH in the presence of asuitable carbon source, nitrogen source, and appropriate vitamins andminerals. The production conditions, which are known in the art, areinfluenced by many factors including the type of fermentor, the mediacomposition, the strain, the pH of the media, the temperature anddissolved oxygen concentration in the bioreactor. The xanthan gumfermentation produces an impure broth, which can comprise up to about 7wt % xanthan gum that must be purified to meet established qualityspecifications for purity, color, flavor, odor and viscosity.

FIG. 1 shows an embodiment of the process for recovering apolysaccharide gum from a first aqueous fluid 8 comprising water andbetween about 1 and 10 wt % of at least one polysaccharide gum (e.g.,xanthan gum, among others) that is substantially dissolved in the fluid.The first aqueous fluid 8 can, in certain embodiments, further compriseother components. For example, when the aqueous fluid is derived from afermentation broth it can comprise unused media components (e.g., carbonsource, among others), cellular debris, other fermentation products ormetabolites. A fermentation broth, a plant extract, or otherpolysaccharide gum solution (e.g., an aqueous solution of commerciallyavailable polysaccharide gum) can be concentrated to produce the aqueousfluid 8. Concentration of a first aqueous fluid 8 (e.g. increasing theconcentration of the polysaccharide gum) can be carried out usingfiltration or other methods known in the art, and the waste stream 6produced by concentration can comprise impurities (e.g., certainimpurities that can accumulate during fermentation). Impurities can besoluble or insoluble. Alternatively a first aqueous fluid 8 can comprisebetween about 1 and 10 wt % of at least one polysaccharide gum in asolution without concentration. For example, a fermentation for xanthangum can be carried out that yields an unconcentrated fermentation brothhaving between about 1 and 10 wt % dissolved xanthan gum that can beused as a first aqueous fluid 8 in the present invention Undissolvedcomponents, such as biomass, among others, can be removed from apolysaccharide gum solution prior to its being used as a first aqueousfluid 8, or prior to its being concentrated for use as a first aqueousfluid 8.

The first aqueous fluid 8 is mixed with an organic non-solvent stream20, which comprises water and a non-solvent of the polysaccharide gumthat is to be recovered. The non-solvent is water miscible and can be anorganic solvent selected from the group consisting of isopropyl alcohol,methanol, ethanol, acetone, other organic solvents of similar polarity,and mixtures of these solvents. When the polysaccharide gum to berecovered is xanthan gum, it is preferred that the organic non-solventstream 20 comprises isopropyl alcohol and water. Preferably the organicnon-solvent stream 20 is recycled from previous polysaccharide gumrecovery processes or from other industrial processes. The organicnon-solvent stream 20 can comprise water and a non-solvent recoveredfrom drying a wet polysaccharide gum (e.g., second fraction) 22,described below, which also yields a first dried polysaccharide gumproduct 28. In addition to water the non-solvent stream 20 can alsocomprise organic non-solvent, which has been recovered from distillationprocesses. Preferably the non-solvent stream 20 is recycled from thedownstream portion of the recovery process. It is mixed with the firstaqueous fluid 8 to produce the first mixture. Preferably, theconcentration of the organic non-solvent in the first mixture 10comprising the first aqueous stream 8 and the organic non-solvent stream20 is at a subprecipitant level. That is, the level of organicnon-solvent in the mixture 10 is below that which would causeprecipitation of the polysaccharide gum. The first mixture 10 isconcentrated to increase the polysaccharide gum concentration. Theorganic non-solvent concentration in the concentrated first mixture 12is below the minimum concentration at which the polysaccharide gumbegins to precipitate. The water and non-solvent removed duringconcentration of the first mixture 10 are components of a stream 11,which can be distilled to recover non-solvent 30. When thepolysaccharide gum being recovered from the aqueous fluid 8 is xanthangum and the organic non-solvent being used is isopropyl alcohol, thesub-precipitant amount of organic non-solvent in the first mixture 10 ispreferably between about 5 and 45% by weight of the first mixture, morepreferably between about 20% and 40%, and most preferably between about30% to 40%.

Concentration of the first mixture can be accomplished by filtering thefirst mixture 10 using microfiltration or by using other methods knownin the art. The first mixture 10, 12, or both can be heat treated at atemperature and for a time sufficient to cause at least some increase inthe viscosity of the polysaccharide gum. The heat treatment can beperformed at least one of before, after, or during concentrating thefirst mixture and before precipitation. Preferably, when xanthan gum isbeing recovered, the first mixture 10, 12, or both is heat treated at atemperature of between about 90° C. and about 125° C. for at least aboutfive minutes, more preferably for at least about 15 minutes.

Following the concentration of the first mixture and optional heattreatment, additional organic non-solvent 30 is mixed with theconcentrated first mixture 12 or 14 (depending on whether a heattreatment is applied) thereby producing a second mixture 16, wherein thesecond mixture 16 comprises (A) a liquid component comprising organicnon-solvent and water, wherein the organic non-solvent concentration inthe second mixture is sufficient to precipitate a majority (e.g.,greater than about 50 wt %) of the polysaccharide gum present in thesecond mixture, and (B) precipitated polysaccharide gum. The water andorganic non-solvent 22, which are driven off during drying of the secondfraction 18 can be condensed and distilled to recover the organicnon-solvent which can be used as a component of the second mixture. Asadditional organic non-solvent is mixed with the first mixture some ofthe polysaccharide gum may precipitate before a precipitateconcentration of non-solvent is achieved throughout the second mixture.Additional non-solvent is preferably the same non-solvent that is acomponent of the organic non-solvent stream, however in certainembodiments it can be a different non-solvent.

The second mixture 16 can be separated into a first fraction 20 and asecond fraction 18, wherein the first fraction 20 comprises a majority(e.g., greater than 50 wt % of the liquid in the second mixture 16) ofthe liquid component (e.g., comprising water and non-solvent) and thesecond fraction 18 comprises substantially all (greater than about 95 wt%) of the precipitated polysaccharide gum. The organic non-solventstream 20 used in the first mixture 10 comprises the separated firstfraction 20 of the separation step, and it can further comprise thestream 22 described above. While the organic non-solvent stream isdepicted in FIG. 1 as being recycled from a polysaccharide recoveryprocess of the present invention, the organic non-solvent stream can bederived from other sources known in the art. For example, the organicnon-solvent stream can comprise products or byproducts of anotherindustrial process that comprise the non-solvent.

The second fraction 18 can be dried to produce a first driedpolysaccharide gum product 28 (e.g., comprises less than about 12 wt %water). Preferably before the second fraction 18 is dried, it is washedwith an organic non-solvent or a first solution comprising water and anorganic non-solvent, wherein the concentration of the organicnon-solvent in the first solution is greater than the concentrationsufficient to precipitate a majority of the polysaccharide gum. Theresidual water and organic solvent 22 driven off by drying of the secondfraction 18 can be condensed and can be a component of the organicnon-solvent stream 20 used in preparing the first mixture. Part or allof the water and non-organic solvent 20 can be recovered from theseparation step (e.g., directly from the first fraction), from thedrying step (e.g., stream 22), and/or from the non-solvent component 30of the non-solvent distillation. Optionally, at least a portion ofstream 11 can be distilled to recover non-organic solvent 30, which canbe used to precipitate the polysaccharide gum 16 from the first mixture.While the additional amount of organic non-solvent that is added to theconcentrated first mixture is depicted in FIG. 1 as being recycled fromdistillation of non-solvent 11 from a polysaccharide recovery process ofthe present invention, the organic non-solvent can be derived from othersources. For example, it can be the product or byproduct of distillationfrom another industrial process. The methods described above for therecovery of a polysaccharide gum can be carried out as batch orcontinuous processes.

Preferably when the polysaccharide gum being recovered in processes ofthe present invention is xanthan gum, and when the first driedpolysaccharide gum product 28 is rehydrated it has a viscosity that isat least 10% greater than that of a rehydrated dried xanthan gum productwhich has been prepared by another method (e.g., an alternative method).A process flow diagram for such a second method is shown in FIG. 2.

A second aqueous fluid 40 comprising water and xanthan gum and havingthe same composition as that provided for preparing the first driedpolysaccharide gum product 28 is heated treated at the same temperatureand for the same duration as the first mixture 10 in preparing the firstdried polysaccharide gum 28. Sufficient organic non-solvent 54 is mixedwith the heat-treated second aqueous fluid 42 to produce a third mixture44 comprising (A) a liquid component comprising organic non-solvent andwater, and (B) a second precipitated xanthan gum. The water in theliquid component is water that was present in the second aqueous fluid40, and the organic non-solvent concentration in the third mixture 44 issufficient to precipitate a majority (greater than about 50 wt %) of thexanthan gum present in the third mixture 44. The third mixture 44 isseparated into an A fraction 50 and a B fraction 46, wherein the Afraction comprises a majority (e.g., greater than 50 wt % of the liquidpresent in the third mixture) of the liquid component (e.g., comprisingwater and non-solvent), and the B fraction 46 comprises substantiallyall (e.g., greater than about 95 wt %) of the second precipitatedxanthan gum. The B fraction 46 is dried to produce a second driedxanthan gum product 48. The water and organic non-solvent 52 driven offfrom drying can be distilled to recover the organic non-solvent 54,which can be used in subsequent rounds of the process to precipitate apolysaccharide gum from solution. Though the organic non-solvent used toprecipitate the second xanthan gum is depicted in FIG. 2 as beingrecycled from the alternative polysaccharide recovery process, thedistilled organic non-solvent can come from other industrial processes.

Most commercial xanthan gums undergo a heat treatment in order for themto provide a higher viscosity per unit solids. Thus, xanthan gum andcertain other polysaccharide gums are typically heat treated in aqueoussolution during industrial processing. Heat treatment causes changes inthe xanthan gum structure, which increases the viscosity of the finishedgum by anywhere from 20 to 50%. There can be wide variability in theincrease of viscosity attained in xanthan gum products produced fromdifferent aqueous solutions despite their undergoing identical heattreatments, particularly when the aqueous solutions are fermentationbroths.

As stated above, industrial processes typically involve heat treatmentof aqueous solutions of polysaccharide gums. Embodiments of the presentinvention involve heat treatment of a mixture comprising an aqueouspolysaccharide gum solution and a water miscible non-solvent. Theincrease in viscosity attained in xanthan gum products of certainembodiments of the present invention can be more consistent than theviscosity attained using processes in which only the aqueous solution isheat treated. Certain embodiments of the present invention involvingheat treatment can further produce xanthan gum product, which can bedried in the form of somewhat discrete fibrous strands, as opposed togelatinous balls which can be produced from certain industrial processescurrently in use, and which are less desirable.

Certain processes being used in industry result in polysaccharide gumproducts with various shortcomings, including the high cost ofproduction. One of the key cost drivers in xanthan gum purificationprocesses involves the expense associated with the organic non-solventused in precipitation. Non-solvent distillation (e.g., IPA distillation)costs are high due to the relatively low yield of gum produced fromthese processes, and due to the energy associated with the distillationof non-solvent mixtures, which contain a large amount of impurities(e.g., non-IPA components). Certain embodiments of the present inventioncan reduce the amount of non-solvent that requires distillation, andthus the losses associated with distillation for the recovery of thenon-solvent can be reduced, and the energy costs associated withdistillation can be decreased.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples, which follow, representtechniques discovered by the inventor to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

In the following examples heat treatments of xanthan gum were performedon raw fermentation broths and other aqueous solutions of xanthan gum ina lab Parr pressure reactor for 30 minutes, unless otherwise specified.After heat treatment, the gum was precipitated from the broth byinjecting a stream of broth along with a stream of isopropyl alcohol(IPA) into the suction side of a lab homogenizer. The precipitate wascollected in a lab basket-type centrifuge. Excess liquid was removed bypressing the gum between sheets of blotter paper. The gum was driedovernight in a solvent-proof forced-air oven at 33° C.

For studies on the effects of gum concentration, concentrations wereincreased by microfiltration, or decreased by the addition of filtratefrom microfiltration. In this way, all characteristics of the broth wereheld constant save for gum concentration.

For comparisons of levels of isopropyl alcohol (IPA), either filtrate,pure IPA, or a mixture of filtrate and IPA was added to the broth sothat final gum concentrations were the same.

All viscosity measurements were made on the rehydrated final, driedproduct. The dry gum was rehydrated in an aqueous solution containing0.1% NaCl and 0.015% CaCl₂2H₂O, at 0.25% gum concentration, with mixing,for 1 hour. Viscosities were measured using a DVII Brookfield Viscometerwith the small sample adapter and #18 spindle, at 0.6 rpm (approx. 0.4s⁻¹ shear rate). All viscosities referred to in these examples are theviscosities of gum after it has been heat-treated, precipitated, dried,and then rehydrated to 0.25% ds.

EXAMPLE 1 Effect of Isopropanol Content During Heat Treatment on theViscosity of Rehydrated Xanthan Gum

FIG. 3 shows the effect of IPA content in the fermentation broth duringheat treatment on the viscosity of the re-hydrated gum. Each broth washeat treated at 90° C. for 20 minutes. The gum viscosity increasedsteadily as IPA concentration in the broth increased.

Rehydrated gum viscosity continues to increase with increases in IPAcontent in the broth during heat treatment through at least 30%, byweight, of the broth. FIG. 3 illustrates the increase in xanthan gumviscosity when IPA was increased from 0%, through 15%, up to 30%.

EXAMPLE 2 Effect of IPA Concentration in the Broth, and Temperature,During 30 min Heat Treatments on the Viscosities of the Xanthan Gumafter Rehydration

FIG. 4 shows the effect of temperature during heat treatment on finalgum viscosity. There exists a minimum temperature necessary for optimumviscosity development. Above this minimum, and especially with high IPAconcentrations in the fermentation broth, the final gum viscositiesremain high. That is, it is not necessary to hit the optimum temperatureto attain high gum viscosity, only to exceed the minimum temperature.This figure also illustrates the effect of IPA concentration in thebroth on the viscosity of the dry gum. Increasing IPA concentrationthrough about 30% significantly increases gum viscosity.

EXAMPLE 3 Effect of Increasing Xanthan Gum Concentration in Broth duringHeat Treatment

FIGS. 5 and 6 show that increases in gum concentration in the brothduring heat treatment increase the viscosity of the final gum. This istrue whether the fermentation broth contains IPA during heat treatmentor not, but is amplified with the presence of IPA. FIG. 5 shows theeffect in absence of any IPA during heat treatment; and FIG. 6 shows theeffect when the broth contained 30% IPA during heat treatment.

The effect of increasing gum concentration during heat treatment reachesa maximum with about 3% gum. With further increases in gumconcentration, no advantage is gained in final product viscosity. On theother hand, the gum concentration can be increased to 6.6% and higherbefore heat treatment without compromising the quality of the product.This offers clear advantages in, for example, minimizing the amount ofnon-solvent needed to precipitate the gum.

EXAMPLE 4 Effect of Source of IPA Used in the Heat Treatment of XanthanGum

Whether the IPA in the broth during heat-treatment is freshly distilled,or originates from a recycle stream in the process, has little effect onthe final gum viscosity. FIG. 7 shows a comparison of gum viscosity fromfermentation broths heat-treated with the addition of pure (99%) IPA,and with the addition of aqueous IPA collected after separatingprecipitated gum from filtrate in a previous treatment. The fermentationbroth containing the filtrate perhaps requires a few degrees higher toreach its minimum for viscosity development, but the viscosities of thegums treated above this minimum are very similar. In fact, the productheat-treated with filtrate appears to be more robust to highertemperature during treatment.

EXAMPLE 5 Effect on Final Xanthan Gum Viscosity Depending on Length ofHeat Treatment

Final gum viscosity appears to be largely insensitive to treatment time.FIG. 8 shows the viscosities of gums that were held at treatmenttemperature for times as short as 10 minutes, and as long as 30 minutesand in the presence of 30% isopropanol. There is little difference amongthem.

The viscosity-enhancing effects of these alcohol heat-treatments aremost pronounced with “low quality” gum. Quality of xanthan gum isassessed by its ability to build viscosity in water, at lowconcentrations. High viscosity gums command a premium price in theindustry. The viscosity of the raw fermentation broth is a goodpredictor of gum viscosity after heat-treatment, precipitation anddrying. The molecular weight of the gum is also a predictor of relativesolution viscosity of xanthan gum (as well as other polymers).

EXAMPLE 6 Viscosities of Raw Fermentation Broth As Compared ToViscosities of Xanthan Gums Recovered from Dilute Solution

FIG. 9 compares fermentation broths heat-treated in a conventionalmanner, and heat treated after the addition of IPA (30%). Theviscosities of the conventionally-heat-treated gums correlate with brothviscosities, and with gum molecular weights. The concentration of thexanthan gums in solution was 2.2%. The gums heat-treated with IPA allhave much higher viscosities. Viscosities were measured using aBrookfield viscometer at 60 rpm. The % increase in viscosity due to thepresence of IPA is most pronounced for the lowest viscosity broth(lowest molecular weight gum). As gum “quality” improves, the ability ofIPA to enhance viscosity is diminished. Still, the top quality gum,which at 944 cps viscosity after conventional heat treatment would beconsidered at the high end of commercial products, experiences aviscosity increase of more than 40% when heat-treated in the presence ofIPA.

The viscosity-enhancing effect of IPA during heat-treatment is notlimited to the treatment of raw fermentation broths of xanthan gum. Theviscosities of a number of commercially available, food-grade xanthangum products (e.g., Keltrol, Keltrol RD, ADM 200, Rhodigel and RhodigelUltra) were significantly increased by heat-treating them with alcohol.To do this, they were dissolved at 2.5% concentration in a 90/10 mixtureof water and IPA, and then heated at 95° C. for 30 minutes. They werethen precipitated and dried. The solution viscosities of these productswith and without the IPA heat treatment are compared in FIG. 10. As acontrol, a sample of xanthan gum (e.g., lab generated) which had alreadybeen subjected to heat-treatment in the presence of 30% IPA,precipitated and dried, was treated in the same way as the commercialgums.

The viscosities of all the commercial xanthan gums were significantlyincreased by the alcohol-heat-treatment. The only gum to lose viscosityas a result of the heat treatment was the lab sample, which hadpreviously been treated with a higher concentration of alcohol.

The significance of this finding is that “low quality” xanthan gumcurrently excluded from the premium markets can be easily converted to ahigh viscosity, premium product.

EXAMPLE 7 Conventional Process

A starting xanthan gum broth was prepared by dissolving 45 pounds ofRodigel EZ in city water to a concentration of 3.5% gum by weight. Thebroth was pumped through a continuous heat treatment at 99 degrees C.with a residence time of 20 minutes. The heat treated broth was mixedwith sufficient 83.1% isopropyl alcohol to cause precipitation resultingin a liquid mixture that was 56.9% isopropyl alcohol by weight. Thexanthan fibers were separated from the liquid with a centrifuge and thefiltrate collected for future recycle. The fibers were dried andanalyzed for viscosity. The following table documents the mass balancethroughout the process:

TABLE 1 Trial #1 With No Alcohol Recycle Pounds Gum Alcohol Water TotalFermentation Product 45.0 0.0 1240.7 1285.7 First Concentrate 45.0 0.01240.7 1285.7 Recycled Alcohol 0.0 0.0 0.0 0.0 Mix Product 45.0 0.01240.7 1285.7 Second Permeate 0.0 0.0 0.0 0.0 Second Concentrate 45.00.0 1240.7 1285.7 Fresh Alcohol 0.0 2239.2 455.4 2694.5 Separation Feed45.0 2239.2 1696.1 3980.2 Separation Filtrate 0.0 2232.8 1658.5 3891.3Dryer Feed 45.0 6.3 37.6 88.9The simulated broth was not concentrated prior to precipitation.Therefore, the first concentrate, the mix product, and the secondconcentrate were identical. The amount of fresh alcohol required tocause precipitation at 56.9% isopropyl alcohol concentration was 2.1pounds of source alcohol per pound of water in the simulatedfermentation broth. The resulting dried xanthan gum had a viscosity of850 centipoise as measured by a Brookfield viscometer with a SS#18spindle at 0.6 rpm at a 0.25% gum concentration.

EXAMPLE 8 Broth Concentration and Alcohol Recycle

A starting Xanthan Gum broth was prepared by standard fermentationpractice using Xanthomonas bacterium to achieve a gum concentration of3.15% by weight. The broth was microfiltered through 0.05 micron ceramicmembranes to concentrate the broth to 7.1% gum by weight. Centrifugefiltrate (alcohol recycle) from Example 7 was mixed with theconcentrated broth. The resulting mixture was re-concentrated with 0.05micron ceramic membranes to a gum concentration of 5.1% by weight. There-concentrated broth with an alcohol concentration of 31.8% by weightwas pumped through a continuous heat treatment at 99 degrees C. with aresidence time of 20 minutes. The heat treated broth was mixed withsufficient 83.1% isopropyl alcohol to cause precipitation resulting in aliquid mixture that was 67.2% isopropyl alcohol by weight. The xanthanfibers were separated from the liquid with a centrifuge and the filtratecollected for future recycle. The fibers were dried and analyzed forviscosity. The following table documents the mass balance throughout theprocess:

TABLE 2 Trial #2 With Alcohol Recycle From Trial #1 Pounds Gum AlcoholWater Total Fermentation Product 49.5 0.0 1521.9 1571.4 FirstConcentrate 49.5 0.0 650.6 700.1 Recycled Alcohol 0.0 464.2 344.8 809.0Mix Product 49.5 464.2 995.5 1509.1 Second Permeate 0.0 171.9 368.6540.5 Second Concentrate 49.5 292.3 626.9 968.7 Fresh Alcohol 0.0 1700.7345.9 2046.6 Separation Feed 49.5 1993.0 972.8 3015.3 SeparationFiltrate 4.4 1979.1 926.4 2909.9 Dryer Feed 45.1 13.9 46.4 105.4The amount of fresh alcohol required to cause precipitation at 67.2%isopropyl alcohol concentration was 3.15 pounds of source alcohol perpound of water in the first concentrate. The resulting dried xanthan gumhad a viscosity of 1180 centipoise as measured by a Brookfieldviscometer with a SS#18 spindle at 0.6 rpm at a 0.25% gum concentration.If centrifuge filtrate from Example 7 had not been mixed andre-concentrated, the amount of alcohol required to precipitate at 67.2%alcohol concentration would have been 4.23 pounds of source alcohol perpound of water in the first concentrate. If the conventional process hadbeen used on the above fermentation broth, 6432.2 pounds of sourcealcohol would have been required to precipitate at 67.2% alcoholconcentration. The claimed process reduced source alcohol usage by 68%.The dried gum produced by the claimed process had a viscosity 39%greater than a competitive gum produced through a conventional process.

EXAMPLE 9 Broth Concentration and Alcohol Recycle

A starting xanthan gum broth was prepared by standard fermentationpractice using Xanthomonas bacterium to achieve a gum concentration of3.29% by weight. The broth was microfiltered through 0.05 micron ceramicmembranes to concentrate the broth to 7.7% gum by weight. Centrifugefiltrate (alcohol recycle) from Example 8 was mixed with theconcentrated broth. The resulting mixture was re-concentrated with 0.05micron ceramic membranes to a gum concentration of 4.84% by weight. There-concentrated broth with an alcohol concentration of 39% by weight waspumped through a continuous heat treatment at 99 degrees C. with aresidence time of 20 minutes. The heat treated broth was mixed withsufficient 83.1% isopropyl alcohol to cause precipitation resulting in aliquid mixture that was 63.0% isopropyl alcohol by weight. The xanthanfibers were separated from the liquid with a centrifuge and the filtratecollected for future recycle. The fibers were dried and analyzed forviscosity. The following table documents the mass balance throughout theprocess:

TABLE 3 Trial #3 With Alcohol Recycle From Trial #2 Pounds Gum AlcoholWater Total Fermentation Product 44.5 0.0 1308.1 1352.6 FirstConcentrate 44.5 0.0 531.8 577.4 Recycled Alcohol 1.1 486.3 228.8 715.1Mix Product 45.6 486.3 760.6 1292.5 Second Permeate 0.0 136.7 213.7350.4 Second Concentrate 45.6 349.6 546.9 942.1 Fresh Alcohol 0.0 889.7180.9 1070.6 Separation Feed 45.6 1239.3 727.8 2012.7 SeparationFiltrate 4.2 1231.3 691.8 1927.3 Dryer Feed 41.4 8.0 35.9 85.4The amount of fresh alcohol required to cause precipitation at 63.0%isopropyl alcohol concentration was 2.01 pounds of source alcohol perpound of water in the first concentrate. The resulting dried xanthan gumhad a viscosity of 1390 centipoise as measured by a Brookfieldviscometer with a SS#18 spindle at 0.6 rpm at a 0.25% gum concentration.If centrifuge filtrate from Example 8 had not been mixed andre-concentrated, the amount of alcohol required to precipitate at 63.0%alcohol concentration would have been 3.13 pounds of source alcohol perpound of water in the first concentrate. If the conventional process hadbeen used on the above fermentation broth, 4100 pounds of source alcoholwould have been required to precipitate at 63.0% alcohol concentration.The claimed process reduced source alcohol usage by 74%. The dried gumproduced by the claimed process had a viscosity 64% greater than acompetitive gum produced through a conventional process.

EXAMPLE 10 Broth Concentration and Alcohol Recycle

A starting xanthan gum broth was prepared by standard fermentationpractice using Xanthomonas bacterium to achieve a gum concentration of3.10% by weight. The broth was microfiltered through 0.05 micron ceramicmembranes to concentrate the broth to 6.83% gum by weight. Centrifugefiltrate (alcohol recycle) from Example 9 was mixed with theconcentrated broth. The resulting mixture was re-concentrated with 0.05micron ceramic membranes to a gum concentration of 4.62% by weight. There-concentrated broth with an alcohol concentration of 36.4% by weightwas pumped through a continuous heat treatment at 99 degrees C. with aresidence time of 20 minutes. The heat treated broth was mixed withsufficient 83.1% isopropyl alcohol to cause precipitation resulting in aliquid mixture that was 56.8% isopropyl alcohol by weight. The xanthanfibers were separated from the liquid with a centrifuge and the filtratecollected for future recycle. The fibers were dried and analyzed forviscosity. The following table documents the mass balance throughout theprocess:

TABLE 4 Trial #4 With Alcohol Recycle From Trial #3 Pounds Gum AlcoholWater Total Fermentation Product 39.6 0.0 1237.8 1277.4 FirstConcentrate 39.6 0.0 541.5 581.1 Recycled Alcohol 1.6 457.0 257.0 715.6Mix Product 41.2 457.0 798.5 1296.7 Second Permeate 0.0 147.4 257.5404.9 Second Concentrate 41.2 309.6 541.0 891.8 Fresh Alcohol 0.0 548.4111.5 659.9 Separation Feed 41.2 858.0 652.5 1551.7 Separation Filtrate6.0 853.9 621.8 1481.7 Dryer Feed 35.2 4.1 30.7 70.0

The amount of fresh alcohol required to cause precipitation at 56.8%isopropyl alcohol concentration was 1.22 pounds of source alcohol perpound of water in the first concentrate. The resulting dried xanthan gumhad a viscosity of 1360 centipoise as measured by a Brookfieldviscometer with a SS#18 spindle at 0.6 rpm at a 0.25% gum concentration.If centrifuge filtrate from Example 9 had not been mixed andre-concentrated, the amount of alcohol required to precipitate at 56.8%alcohol concentration would have been 2.16 pounds of source alcohol perpound of water in the first concentrate. If the conventional process hadbeen used on the above fermentation broth, 2673.3 pounds of sourcealcohol would have been required to precipitate at 56.8% alcoholconcentration. The claimed process reduced source alcohol usage by 75%.The dried gum produced by the claimed process had a viscosity 60%greater than a competitive gum produced through a conventional process.

EXAMPLE 11 Broth Concentration and Total Alcohol Recycle

A starting xanthan gum broth is prepared by standard fermentationpractice using Xanthomonas bacterium to achieve a gum concentration of3.00% by weight. The broth is microfiltered through 0.05 micron ceramicmembranes to concentrate the broth to 7.50% gum by weight. All of thecentrifuge filtrate (alcohol recycle) from a previous batch is mixedwith the concentrated broth. The resulting mixture is re-concentratedwith 0.05 micron ceramic membranes to a gum concentration of 7.50% byweight. The re-concentrated broth with an alcohol concentration of 35.4%by weight is pumped through a continuous heat treatment at 99 degrees C.with a residence time of 20 minutes. The heat treated broth is mixedwith sufficient 83.1% isopropyl alcohol to cause precipitation resultingin a liquid mixture that is 55.0% isopropyl alcohol by weight. Thexanthan fibers are separated from the liquid with a centrifuge and thefiltrate is recycled while the fibers are dried. The following tabledocuments the mass balance throughout this process:

TABLE 5 Prophetic Total Alcohol Recycle Pounds Gum Alcohol Water TotalFermentation Product 40.0 0.0 1293.3 1333.3 First Concentrate 40.0 0.0493.3 533.3 Recycled Alcohol 1.0 461.7 349.8 811.5 Mix Product 41.0461.7 843.1 1344.8 Second Permeate 0.0 282.4 515.7 798.1 SecondConcentrate 41.0 179.3 327.4 546.7 Fresh Alcohol 0.0 293.9 59.8 353.7Separation Feed 41.0 473.2 387.2 900.4 Separation Filtrate 1.0 461.7349.8 811.5 Dryer Feed 40.0 11.6 37.3 88.9

The amount of fresh alcohol required to cause precipitation at 55.0%isopropyl alcohol concentration is 0.72 pounds of source alcohol perpound of water in the first concentrate. The resulting dried xanthan gumhas a viscosity of 1300-1400 centipoise when measured by a Brookfieldviscometer with a SS#18 spindle at 0.6 rpm at a 0.25% gum concentration.If centrifuge filtrate is not mixed and re-concentrated, the amount ofalcohol required to precipitate at 55.0% alcohol concentration will be1.96 pounds of source alcohol per pound of water in the FirstConcentrate. If the conventional process is used on the abovefermentation broth, 2531.4 pounds of source alcohol is required toprecipitate at 55.0% alcohol concentration. The claimed process thusreduces source alcohol usage by 86%. The dried gum produced by theclaimed process has a viscosity 53-65% greater than a competitive gumproduced through a conventional process.

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of preferred embodiments, it will be apparent tothose of skill in the art that variations may be applied to thecompositions and methods and in the steps or in the sequence of steps ofthe method described herein without departing from the concept, spiritand scope of the invention. More specifically, it will be apparent thatcertain agents, which are chemically related, may be substituted for theagents described herein while the same or similar results would beachieved. All such similar substitutes and modifications apparent tothose skilled in the art are deemed to be within the spirit, scope andconcept of the invention as defined by the appended claims.

1. A xanthan gum prepared by a method comprising: providing an aqueousfluid comprising water and between about 1 wt % and 10 wt % xanthan gum,wherein the xanthan gum is substantially dissolved in the aqueous fluid,mixing the aqueous fluid and an organic non-solvent stream comprisingwater and an organic non-solvent of xanthan gum, thereby producing afirst mixture, wherein the first mixture comprises a sub-precipitantconcentration of the organic non-solvent; concentrating the firstmixture, thereby increasing the xanthan gum concentration, wherein afterconcentrating the organic non-solvent concentration in the first mixtureis below the minimum concentration at which the xanthan gum begins toprecipitate; heating the first mixture to a temperature of between about90° C. and about 125° C. for at least about five minutes; mixing anadditional amount of organic non-solvent with the first mixture, therebyproducing a second mixture, wherein the second mixture comprises (A) aliquid component comprising organic non-solvent and water, wherein theorganic non-solvent concentration in the second mixture is sufficient toprecipitate a majority of the xanthan gum present in the second mixture,and (B) precipitated xanthan gum; separating the second mixture into afirst fraction and a second fraction, wherein the first fractioncomprises a majority of the liquid component and the second fractioncomprises substantially all of the precipitated xanthan gum; and dryingthe second fraction to produce a first dried xanthan gum product;wherein the first dried xanthan gum product, when rehydrated in water ata concentration of 0.25%, has a viscosity in excess of 800 cps whenmeasured on a Brookfield viscometer with a #4 spindle at 60 rpm and 75°F., and has a viscosity that is at least 10% greater than that of arehydrated dried xanthan gum product prepared by a method comprising:providing a second aqueous fluid comprising water and between about 1 wt% and 10 wt % xanthan gum, wherein the xanthan gum is substantiallydissolved in the aqueous fluid; heat treating the second aqueous fluidat a temperature of between about 90° C. and about 125° C. for at leastabout five minutes; mixing organic non-solvent with the heat-treatedsecond aqueous fluid, thereby producing a third mixture, wherein thethird mixture comprises (A) a liquid component comprising organicnon-solvent and water, wherein the organic non-solvent concentration inthe third mixture is sufficient to precipitate a majority of the xanthangum present in the third mixture, and (B) a second precipitated xanthangum; separating the third mixture into an A fraction and a B fraction,wherein the A fraction comprises a majority of the liquid component andthe B fraction comprises substantially all of the second precipitatedxanthan gum; and drying the B fraction to produce a second dried xanthangum product.
 2. The xanthan gum of claim 1, wherein the organicnon-solvent stream of the method comprises the first fraction.
 3. Thexanthan gum of claim 1, wherein the organic non-solvent of the method isisopropyl alcohol and the sub-precipitant amount of organic non-solventin the first mixture is between about 5 and 45% by weight of the firstmixture.
 4. The xanthan gum of claim 3, wherein the sub-precipitantamount of organic non-solvent in the first mixture is between about 20%and 40% by weight of the first mixture.
 5. The xanthan gum of claim 3,wherein the sub-precipitant amount of organic non-solvent in the firstmixture is between about 30% and 40% by weight of the first mixture.